1. Field of the Invention
The present invention relates to piping in association with subsea oil and gas production. More particularly, the present invention the relates to safety relief valves and processes which serve to avoid the application of excessive pressures within subsea piping. Additionally, the present invention relates to safety relief valves and processes that are directly associated with the chokes associated with subsea piping so as to effectively release excess pressures.
2. Description of Related Art Including Information Disclosed Under 37 CFR 1.97 and 37 CFR 1.98.
Subsea system are usually designed to work across high pressure differentials (e.g., full wellhead shut-in pressure versus operating flow pressure) even when normal operating flow pressure is only a small fraction of full wellhead shut-in pressure, which dramatically increases project capital expenditures. Subsea systems can comprise protection systems to deal with occasional high pressure differentials, for example, by retaining high pressure within a section of the system capable of withstanding the pressure, which prevents the remainder of the system from being exposed to pressure which may exceed its pressure rating. Thus, the protection systems safeguard equipment of the subsea system as well as maintain safe operation of the subsea system, by protecting the equipment from excessive pressure (e.g., pressure exceeding its pressure rating) that might compromise the operation of the equipment.
In the oil and gas industry, production fluid pipelines downstream of the wellhead are generally thin-walled in order to minimize the cost of the pipeline. It is therefore necessary that such pipelines be protected against excessive pressure that might rupture the pipe, which would be very expensive to replace and cause environmental pollution. A conventional system used to protect pipelines from over-pressure is the high integrity protection system (HIPS). This is typically an electro-hydraulic system employing pressure sensors to measure the pressure in the pipes which are used through the electronics of a control module to control the closure of a production pipe HIPS valve. This arrangement retains the high pressure within a short section of pipeline between the production tree and the HIPS valve which is capable of withstanding the pressure. This prevents the main, thinner-walled section of the pipeline from being exposed to pressure levels which may exceed the pipeline's pressure rating.
Unfortunately, such HIPS systems are essentially in the nature of an on/off switch. This is a very complicated system and acts as a fast response valve. When the system senses the pressure is too high, it simply shuts off the system. If it senses pressure is critical, it will turn off.
Conventional subsea piping also can include a choke. A choke facilitates the ability to pass drilling mud, and other abrasive components, therethrough. The conventional choke is relatively slow. It was movable through a wide variety of positions in a ratcheting fashion. As such, the choke is not very fast acting when it is necessary to accommodate high pressures that may be occurring to the system.
In the past, various patents have issued relating to such safety relief valves. For example, U.S. Pat. No. 3,977,423, issued on Aug. 31, 1976 to A. H. Clayton, describes a valve control apparatus and method. This method serves to control a fluid pressure-actuated valve. The valve has an inlet pressure and an outlet pressure that are applied to control and limit the valve outlet pressure and to substantially reduce the fluid pressure applied to the valve actuating means when the valve inlet pressure is below a preselected safe value.
U.S. Pat. No. 4,200,116, issued on Apr. 29, 1980 to F. Gemignani, describes a device for sensing pressure and governing the operation of safety valves. This control device comprises a pair of chambers, each connected to the vessel to be protected and provided with respective valves. The first chamber is connected also to the cylinder of the safety valve via the first valve so that, when an excessive pressure in the vessel develops, the first chamber closes the connection between the vessel and the control cylinder while the second chamber vents the control cylinder to the atmosphere.
U.S. Pat. No. 4,747,853, issued on May 31, 1988 to Haslett et al., discloses a pressure control arrangement for a fluid line in a system. This pressure control arrangement has a normally open valve, a flow restricting member, and a pressure sensor disposed in the fluid line. The pressure sensor is disposed upstream of the flow restricting member and is arranged to sense the pressure in the line and to actuate the valve to close the line in the event of the sensed pressure exceeding a predetermined limit. The predetermined limit is above the normal operating pressure range of the fluid line but below the maximum overpressure to which there is a risk of the line being subject. The portion of the fluid line upstream of the flow restricting member is constructed to have a maximum design pressure at least equal to the maximum overpressure.
U.S. Pat. No. 5,063,956, issued on Nov. 12, 1991 to Borcuch et al., discloses a fluid delivery pressure control system to maintain a set delivery pressure at varying demand. The system includes a fluid-loaded, self-operated main regulator. The system includes a flow restrictor for metering the loading fluid flow, a back-pressure regulator for controlling the loading fluid pressure, and a temperature-actuated regulator for venting loading fluid when the process fluid temperature varies from a selected range.
U.S. Pat. No. 7,044,156, issued on May 16, 2006 to D. Webster, describes a pipeline protection system that comprises a hydraulically-actuated valve operable to switchably prevent a flow of fluid from a first section of the pipeline to a second section of the pipeline. There is a hydraulic fluid source for supplying hydraulic fluid to the hydraulically-actuated valve to enable actuation thereof. A vent is provided for venting hydraulic fluid from the hydraulically-actuated valve. The hydraulically-actuated valve is connected to the vent via a differential pressure valve to control venting of the hydraulically-actuated valve. A pressure transfer barrier with a first port is connected to the first section of the pipeline and a second port is connected to the differential pressure valve. The differential pressure valve is supplied with hydraulic fluid at a reference pressure. If the pressure of fluid in the first section of pipeline exceeds the reference pressure of the hydraulic fluid supplied to the differential pressure valve, the differential pressure valve is caused to be in an open state, thereby causing the hydraulic pressure in the hydraulically-actuated valve to be released via the vent.
U.S. Pat. No. 7,284,563, issued on Oct. 23, 2007 to Partridge et al., describes a surge relief apparatus for sensing, tracking and responding to pressure changes in a flow system. The apparatus includes a fluid storage tank that is in fluid communication with the flow system. The apparatus also includes a control valve that is connected to the fluid storage tank. The control valve compensates for pressure in response to pressure change in the flow system. The control valve also controls the rate of pipeline pressure rise in the flow system. The surge relief apparatus also includes a hydraulic accumulator in fluid communication with the control valve along with a surge relief valve in fluid communication with the accumulator.
U.S. Pat. No. 7,905,251, issued on Mar. 15, 2011 to S. F. Flanders, teaches a high integrity protection system for protection of a pipe downstream of a wellhead. There is an inlet connected to the wellhead and an outlet connected to the downstream pipe. Two sets of two series-connected surface safety valves are in fluid communication with the inlet and outlet. The sets are in parallel fluid flow relation to each other. Either one or both of the sets of surface safety valves are operable as a flowpath for fluids entering the inlet and passing through the outlet to the downstream pipe. Two vent control valves are connected to piping intermediate one set of series-connected surface safety valves. The vent control valves are in fluid communication with a vent line. Upon opening of a vent control valve, a process pressure between the surface safety valves is vented.
U.S. Patent publication No. 2010/0071775, published on Mar. 25, 2010 to A. J. Ratcliffe, describes a subsea system and method for protecting equipment of a subsea system. This subsea system has a wellbore within a reservoir. Equipment is located downstream of the wellbore. A barrier is connected to the equipment. The equipment is rated for a maximum pressure that is less than a maximum reservoir pressure and equal to or greater than the maximum reservoir pressure less external hydrostatic pressure experienced by the equipment. The barrier is rated for a maximum pressure that is equal to or greater than the maximum reservoir pressure.
It is an object of the present invention to provide a safety relief valve that effectively avoids equipment damage to the subsea equipment.
It is another object of the present invention to provide a safety relief valve apparatus that enhances vessel safety.
It is still another object of the present invention to provide a safety relief valve for subsea equipment that minimizes hydrocarbon release in the subsea environment.
It is still a further object of the present invention to provide a safety relief valve for use with subsea equipment that can effectively avoid underground blowouts and other disastrous equipment.
These and other objects and advantages of the present invention will become apparent from a reading of the attached specification and appended claims.